The elaboration of the acanthor shell of Acanthosentis acanthuri (Acanthocephala)

The periembryonic envelopes of an Eoacanthocephala Acanthosentis acanthuri and their elaboration during embryogenesis are, for the first time, described in this study. In studying the evolution of the "fertilization membrane" in particular, it became evident that slight modifications occur and then the "fertilization membrane derivative" is gradually pushed towards the exterior by the new envelopes secreted by the developing embryo. It therefore forms the outermost envelope surrounding the mature acanthor. In A. acanthuri, a series of more "true" envelopes composed of solid material and separated by fluid granular spaces were observed around the acanthor. A nomenclature is proposed in order to make a clear distinction between the envelopes (E1-E4) and the granular spaces (G1-G4).